1. Field of the Invention
This invention relates to a barium titanate ceramic having a positive temperature coefficient of electric resistance (to be referred to as "PTC ceramic"), and more particularly to a ceramic which maintains a high electric resistance over a wide temperature range and a high temperature coefficient of electric resistance at temperatures just below the aforesaid range.
2. Description of the Prior Art
When a PTC ceramic is used for temperature sensing and electric current limiting, inclusive of current interruption, it is required to simultaneously meet the following two conditions; namely, to maintain a high electric resistance over a wide temperature range and to have a large temperature coefficient of electric resistance at temperatures just below the aforesaid range. For instance, when a ceramic is used to sense the presence of a flame, it is required to keep a high electric resistance as long as flame exists, large or small, and to rapidly decrease its electric resistance upon loss of the flame. However, there has not been any PTC ceramic, heretofore, which satisfactorily meets both of the two conditions.
Therefore, an object of the present invention is to provide an improved PTC ceramic which simultaneously meets the aforesaid two conditions.